The invention concerns a bone implant which contains a magnesium-containing metallic material with reduced corrosion rate and mineral bone cement, as well as methods and a kit for its production.
Often, only a temporary residence of implant material is necessary in the body when using medical implants. In connection with such implantations, for many years research has been done on the development of bioresorbable implant materials in order to eliminate in the future a complex operation for removing implant materials which cannot be decomposed by the body. Bioresorbable materials have the property of being decomposed gradually after implantation in the body. The resulting decomposition products are resorbed by the body to a large extent.
The decomposition of implant materials can occur actively or passively. In case of active decomposition by the organism, the implant material is degraded by enzymatic or cellular mechanisms. This happens, for example, with implant materials of collagen or mineral bone cements on the base of calcium phosphates. The active decomposition of implant materials is desired particularly when the decomposition occurs within the scope of the natural metabolism and is not based on an inflammation reaction.
A passive decomposition occurs with implant materials which are not stable in the biological environment. This passive decomposition is called herein biodegradation. It is typical for the resorbable polymers of which resorbable suture materials are produced, for example. The decomposition of metals which are not stable in the biological environment occurs also passively. This is referred to herein also as corrosion. Corrosion is to be understood in this context as the conversion of metallic materials into their oxides or salts, i.e., into mineral materials. The term biocorrodibility, i.e., corrosion in the biological environment, has been established for the metallic implant materials. The term is in general used for the desired corrosion of a metallic implant in the body. In particular magnesium and its alloys as well as iron and its ignoble alloys are especially considered to be biocorrodible implant metals. Primarily, the magnesium-containing metallic materials increasingly attract great interest because they clearly exhibit higher strength than resorbable polymers and because magnesium is the only technically available metal which is present in the body in larger quantities and which is incorporated in the form of its ion into numerous biochemical reactions. In contrast to the decomposition products of iron, magnesium ions of the corrosion products of magnesium-containing implants can be eliminated from the body easily.
Biocorrodible implants on the basis of resorbable polymers have been available on the market for some time and have gained commercial relevance in some indications with low mechanical load. However, their widespread use is limited by the low biocompatibility of the decomposition products and the mechanical properties of little reproducibility during the course of the decomposition process.
Because especially orthopedic implants must fulfill high mechanical demands, work has been done intensively for several years on implant materials on the basis of biocorrodible metal alloys. In principle, magnesium alloys are very well suited for this use because their decomposition produces preferably decomposition products in the form of magnesium salts which are biocompatible as natural components of the metabolism. In various studies implants of magnesium alloys have been already examined for cardiovascular uses and as bone implants. In this context, good compatibility has been determined in most cases.
However, when magnesium corrodes, a strong gas generation, preferably hydrogen, is noticeable. This leads in case of large-volume bone implants to the formation of gas bubbles in the tissue, because removal is not sufficiently guaranteed. The corrosion occurs, on the one hand, too fast and, on the other hand, in an uncontrolled way, i.e., not evenly from the outside to the inside, but often concentrated at a few locations. A sufficiently reliable adjustment of mechanical properties of an implant over time is thus not possible. Hence, the development of magnesium implants whose corrosion progresses at a reduced level is being worked on. By means of various modifications, the corrosion of magnesium materials, presently too quick and uncontrollable, should be developed to be controllable.
Up to now, two different approaches are pursued in this context. On the one hand, different magnesium alloys are being tested. On the other hand, magnesium and magnesium alloys are provided with coatings which are designed to inhibit the corrosion of the metal
Presently known coatings for inhibiting corrosion of magnesium-based implants are based on the application of polymeric or inorganic layers, the chemical conversion of the metal surface, hot gas oxidation, anodizing, plasma spraying method, varnishes or similar methods
DE 101 63 106 A1 discloses magnesium materials in which the corrosion properties are changed by alloying with halides. It is disadvantageous in this context that not only its corrosion properties are changed by alloying but also the mechanical properties of the material.
DE 10 2006 060 501 A1 discloses methods for producing a corrosion-inhibiting layer on magnesium alloys, in this context, a biocorrodible magnesium alloy is coated by means of an anodic plasma-chemical treatment in an aqueous electrolyte. In this context, the electrolyte contains in one embodiment at least NH3, H3PO4 and H3BO3. In another embodiment, the electrolyte contains NaMnO4 and NH4VO3. In the method the magnesium material is switched as an anode. The anodization occurs by plasma discharge in the electrolyte on the surface of the material part to he coated.
DE 10 2008 043 970 A1 discloses methods for producing corrosion-inhibiting coatings on magnesium materials in which the materials are treated in an aqueous or alcoholic conversion solution and are subjected to anodic oxidation in the conversion solution ions are contained in a concentration of 10−2 mol/l to 2 mol/l. In this context, the ions are selected from at least one of the group K+, Na+, NH4+, Ca2 +, Mg2 +, Zn2 +, Ti4 +, Zr4 +, Ce3 +, PO33−, PO43−, HPO42−, H2PO4−, OH, BO32−, B4O73−, SiO32−, MnO42−, MnO4−, VO3−, WO42−, MoO42−, TiO32−, Se2−, ZrO32− and NbO4−.
In spite of the extensive work in connection with the development of new magnesium alloys, up to now solutions have not been found for the cardiovascular use as stents or for the use as bone implants for lowering the corrosion rate to a sufficiently low level in order to be able to guarantee the mechanical function of the implants for the desired period of >6 weeks for cardiovascular use or also even longer periods of >6 months for use as a bone implant.
Hence, there is still the need for alternative approaches for controlling the corrosion of implants based on magnesium.
It is the object of the invention to provide bone implants with magnesium-containing metallic Materials, which exhibit a high corrosion resistance and improved mechanical properties, and methods and means for their production.